Manual punches are commonly found items in offices and other places of business. These devices typically include one or more rod-shaped punch heads movably mounted in position above an elongated opening into which the edge of the sheet of paper to be punched is received. The punching operation is accomplished by manually depressing a pivoted lever arm which forces the punches heads through the paper. Springs are typically incorporated in the devices to return the punch heads and lever arm to positions ready to accept additional sheets of paper to be punched.
Manual punches of this type vary widely in complexity and capability. The punches may, for example, be specifically adapted to punch one, two, three or more holes at fixed positions in the paper with no provision for adjusting the position of the holes. Some of the more complicated devices enable the punch heads to be moved to desired positions so that the position and number of holes punched may be varied. The devices also typically vary in punching capacity, with light weight devices being capable of punching only a few sheets of paper at the same time and the heavier devices being capable of punching as many as ten or more sheets simultaneously depending upon the thickness of the material being punched.
It can be, and often is, a hard and tedious job to punch holes in large numbers of sheets of paper or the like using manual punches of the type commonly found in present day offices. The tendency is to load the punches to or near their capacity so as to maximize of the number sheets that are punched with one depression of the lever arm. As a result, considerable force must be executed on the lever arm in order to force the punches heads through the paper. If the resistance of the paper to punching is too great, the force that is exerted on the lever arm can bend, loosen or otherwise damage the arm or other components of the punch. Also, in those instances where less than the total number of sheets to be bound together in a report or the like can be punched with one throw of the manual lever arm, it is often difficult to align the sheets consistently for each punch with the result that the pages in the report are out of alignment when bound.
Accordingly, it would be desirable if a punch could be provided which not only enabled a relatively large number of sheets (e.g., 50) to be punched with one operation of the device but which also effected the punching operation automatically without the need for the manual depression of a lever arm.
Automatic punches of various designs have been proposed heretofore, but none such devices has experienced any significant commerical acceptance to date. The problem has been one of delivering, in a reasonably economical structure, the large forces and displacements necessary to activate the punch heads under heavy loads. For example, for 50 sheets of standard paper, total punch head loads in typical three-hole punches can peak over 2000 pounds and require a punch head displacement of 3/8 of an inch.
One prior design uses electrically activated solenoids to push the punch heads through the paper. The solenoids may be adapted to push the punch heads either directly or through a system of lever arms. In either case, devices of this type are disadvantaged because the solenoids cannot easily provide the large punch head forces and displacements needed for heavy loads. While solenoids can be made of a sufficiently large size to provide the necessary force-displacement capabilities, such solenoids would be both bulky and expensive, adding significantly to the size and cost of the device.
Another design utilizes a gear motor to turn a cam shaft to activate the punch heads as cam followers. Like solenoids, however, gear motors are difficult to obtain with sufficient cam torque to drive the cam shaft under a heavy load. Torque load requirements for punches of 10 foot-pounds are not unusual. Gear motors rated at such loads are both large and expensive. Moreover, high gear ratios are typically required which lead to slow operation of cam shaft, at say 1 to 10 revolutions per minute. Each punching operation can thus take several seconds or more to complete.